It is already known in the art to use, at first in papermaking and then, more recently, in rolling mills, rolls with a rotating shell comprising a fixed main shaft in the form of an elongated beam, surrounded by a tubular shell rotatably mounted on the beam about bearings defining an axis of rotation perpendicular to the rolling direction, and bearing on the beam via a plurality of holding means distributed side by side along the length of the beam and centered in an axial bearing plane which corresponds to the plane of transmission of the rolling load when the roll is part of a rolling mill. In fact, the tubular shell, which is relatively thin, is deformable, and by selectively actuating the different holding means, the external face of the roll, for example in a rolling mill of the quarto or sexto type, can be given a profile which allows the deflection of the shaft to be compensated and any faults in the evenness of the surface or in the thickness of the product caused in the course of rolling to be corrected. For this purpose, each means of holding the shell consists of a shoe essentially centered in the bearing plane, disposed between the shell and the support beam and slideably mounted on the said support beam in a radial direction essentially extending in the screw-down plane. Each shoe bears on one side of the internal face of the shell, via a cylindrical bearing face essentially of the same diameter, and on the other side on the support beam via a regulable thrust means, generally a hydraulic jack. It is thus possible to regulate the thrust of each shoe individually in the radial direction, in order to give the tubular shell the desired profile. The tubular shell rotates on the bearing faces of the holding shoes, and it is necessary to introduce continuously, between the bearing face of the shoe and the internal face of the shell, a hydraulic fluid capable of forming a lubricating film.
In general, each holding shoe functions analogously to a hydrostatic bearing, and for this purpose is provided, on its bearing face, with a hydrostatic cavity consisting of a recess opening towards the outside and allowing the lubricating fluid to be distributed in the gap between the bearing face of the shoe and the shell.
It has therefore been proposed, in copending patent application Ser. No. 154,253 filed by the present applicant on Dec. 28, 1987, to connect each holding shoe to means of circulating lubricating fluid in the gap between the shoe and the shell and in the direction of rotation of the latter, in such a way that the holding shoe functions analogously to a hydrodynamic bearing.
To reduce the specific bearing pressure of each shoe on the shell, it has already been proposed, for example in U.S. Pat. No. 3,131,625, to increase the bearing surface of the shoe on the internal face of the shell in such a way that the latter covers a substantial angular sector greater than a quadrant, which may be almost as large as 180.degree.. The shell thus bears on the support beam via actual cushions of fluid, which, furthermore, allow it to be kept essentially centered in the plane of compacting.
In this arrangement, which is provided for the paper industry and is consequently for relatively small pressures, this effect of centering the shell on the holding shoes allows the use of centering bearings placed at either end of the shell to be dispensed with, with the shell bearing on the shaft solely via the shoes.
However, in the case of rolling mills used in metallurgy where the roll is used to apply substantial compacting loads on the product or on a working roll, the shell, which is so mounted that it floats on the shoes, tends to be distorted and to be moved by the rotation of the product or of the working roll, and must therefore be held at each end by centering bearings consisting of an external ring integral with the shell and an internal ring centered on the support beam. However, where substantial rolling loads are involved, these bearings absorb some of the load applied, having the effect, on the one hand, of a perturbation in controlling the distortion of the shell and, on the other hand, of local loads distributed through the system.